texts: Do asteroids originally come from debris of star remnants?

texts: As we know, asteroids can be found in the Kuiper belt and Oort cloud, but surely the Sun only captures them, not produces them. I know that supernovae may produce heavy elements such as oxygen, silicon and iron, which is the common composition of asteroids, so is it true that asteroids are come from star remnants?


texts: What is the shape and size of a gamma ray burst?

texts:
As I understand it, a gamma ray burst is created when a massive star collapses into a black hole.  The poles of the black hole eject a massive burst of energy which we know as gamma ray bursts.

So my question... Are gamma ray burst more or less cylindrical in shape?  Somewhat like a quasar, but in a spectrum that is invisible to our visible spectrum?  And if so, what would the diameter of it be?


texts: Is it easier to see the young moon when it's closer to the sun?

texts:
With the naked eye, would it be easier to see the moon when it's close to the sun, because it might reflect some more light (or not, I'm not sure) or farther from the sun because the sun shines brighter, same with how we can't see the stars?
Also, would it be easier to see it a few minutes after the sun sets and the moon is on the verge of setting, maybe at the +5° on the azimuthal grid?


texts:
I recently came across the book intro to cosmology by j.v. Narlikar, where it mentions about quarks and other star and inadvertently uses mass of sun as reference. I want to know how me measure mass of a star?

I guess from the parallax method we could calculate distance?


texts: Calculating the time a star is at my local meridian based on its right ascension

texts:
I've been watching an astronomy course on YouTube and I'm struggling to calculate stars' positions based on their right ascension.
What I'm trying to achieve: Calculate when a star (Sirius in this example) will be exactly on my local meridian.
What I know: The star's right ascension and the "noon" time (=when the sun will be exactly on my local meridian).
Let's assume we are on March 21st: According to https://stellarium-web.org/ The sun will be on my meridian at 12:10. Sirius's right ascension is 6h46m, which means Sirius should be at the meridian 6h46m later which is 18:56. According to Stellarium Sirius will indeed be at the meridian at 18:52 (I suppose that 4 minute difference is because the sun is already 4 minute behind due to Earth rotation).
But when I try to do the same calculation for today (Feb 10th) I get a 20 minute error.
The "noon" on Feb 10th where I live is at 12:18. We add Sirius' right ascension to get 19:04. But this time we also have to take into account the fact that we are 41 days away from March 21st. Each day the sun falls behind by ~4 minutes, so that's 2h44m. If we add that to 19:04 we get 21:48. So that's the time Sirius should be at my local meridian on this particular day. But Stellarium shows that Sirius will actually be at the meridian at 21:26. So there's 22 minutes error in my calculations for some reason.
I think the root of the error is the 2h44m that I calculated for the sun's position. According to Stellarium the sun's right ascension on that day is 21h38m. Meaning it is 2h22m behind not 2h44m. And that's why I get that 22 minutes error. But I don't understand how it can be 2h22m because Feb/10 is 41 days away from March/21. That means 41x4 = 164 minutes = 2h44m.
What am I missing here?


texts:
I was reading about gravitational lensing. I was just curious to know if there are any formulae or methods to find the angle at which the light deflects due to strong gravitational lensing?

And how far should that massive object be present so that we can observe multiple images of the observing object?


texts: Jupiter FM - What are practical and inexpensive ways for the amateur detection of signals from Jupiter, especially of the transit of her moons?

texts:
What modifications to a standard AM/FM or shortwave radio are needed in order to be able to detect radio-wave signals emitted from Jupiter?

Would it be possible to detect the transit of the major moons and even minor planets (maybe even Ceres and Mars) using this method?


texts: Reason for a correlation between Hot Jupiters and higher metallicity in Kepler data

texts: This question is from an amateur data analysis I did in May 2015 of data from Kepler.nasa.gov/Mission/discoveries. There were 80 Jupiter size planets in the Kepler "confirmed" planet table on this website (through 4/1/15) that had host stars with metallicity data. Of these, 24 stars have [Fe/H}>0.2 and 40 have -0.1<[Fe/H]<+0.2. This is a much higher percentage than the sample as a whole. Would this be strong evidence that high metallicity measurements are due to accretion? Or, do the metallicity measurements given reflect abundance deeper into the star than accretion can count for (ie. higher metallicity stars are more likely to have Jupiters in general)?


texts: How do large solar flares compare to flares on other stars?

texts: Solar are violent releases of solar magnetic energy. Other stars are also known to have magnetic fields, in some cases much stronger than the Sun. How do the largest stellar flares compare to the largest solar flares in terms of energy released? It would also be interesting to normalize the answer by the strength of the magnetic field to be able to compare the efficiency of magnetic energy release on other stars compared to the Sun.


texts: Alien "train" in night sky any one else seen these

texts: on march 1 2020 my sister and I were out about 530am and near the big dipper stars were moving one the two one then two (* ** * **) for about 15 minutes this continues like a train moving they seem to come from nowhere and disappear we had no phone to record it was awesome this was in Bedford Virginia Someone else had to have seen this


texts: The star that died and became the Crab Nebula and Crab Pulsar?

texts: The supernova of this star was witnessed about 1 thousand years ago, and the star's remains are the Crab Nebula and Crab Pulsar. What is this no longer existent star called? How massive was this star? What was the star like before the supernova?


texts: Can a material other than glass be used for making telescope mirrors?

texts:
Although I do know of a few instances where professional or observatory mirrors have been made by alternate materials, it was primarily for targeting specific nuances, like weight reduction and low thermal expansion etc.

I was more keen on finding a material whose primary unique selling point is low cost ;P , keeping in mind a budding amateur astronomer.


texts:
I am studying astrophysics on the side and came across this problem in the textbook:

I am not quite sure how to approach it but I do know I need to account for the Malmquist bias to account for the correct $L$. Is there any insight I can get here?


texts: How to calculate geocentric transformation to heliocentric coordinates?

texts:
I have Sun data (lon+lat+distance) in geocentric coordinates:

but I want to visualize in heliocentric way. How to calculate that?


texts:
I’m trying to calculate visible ISS passes and I need to calculate if the ISS is behind the earth by “drawing” a line between the ISS and the sun and seeing if it crosses earth. I have the ECI position of the ISS, but I don’t have the position of the sun. How do I calculate the suns ECI position given a date and time?

Edit: I need to use c# for this so I can’t use python libraries


texts: Could Planet Nine be a tiny black hole or an exotic compact object such that it escaped detection? What would its bounds be?

texts:
Planet Nine (a variant of the old X-Planet and Tyche-Thelistos hypothesis) proposes a super-earth planet at the edges of the solar system with a mass of around ten Earths. However, given the interest in exotic objects and gravitational variants, maybe it's interesting to study "exotic" scenarios:

Tiny black hole. Using the famous online calculator http://xaonon.dyndns.org/hawking/, for ten earth masses, we get a 89 mm black hole. Temperature about 2 mK! How can we put bounds on this scenario?
An exotic compact object. Of course, we have no evidence so far of general relativity modifications of gravity, but if not a black hole but another "thing" (a gravastar, a quark star, a preon star,...), I find hard to estimate how could we be sure to give up experimentally these examples.

Of course, the real thing is to think something less exotic (I am not sure how to differentiate the P9 hypothesis from a swarm of thousands of ETNO dwarf planet-like or planetesimal-like, but the real issue is how to test these alternative models and if these could affect what we know about the origin and formation of the solar system and its actual current structure, any hint to this in the answer to above exotic cases would also welcome).


texts: How many earths fit in the observable universe?

texts:
I was pondering our insignificance, when I wondered - how much smaller is our planet then the (observable) universe? And being as I don't know how to do the math, I'm asking it here.

So how many of our planet (in space it occupies - i.e. ignoring space between the space between the spheres) can fit inside the known/observable universe?


texts:
For those that haven't seen this link - please have a look as it's a an awe-inspiring 360 interactive panormic image of the milky way (may need a bit of time to load though!). I've found myself idly browsing it several times and as an astronomy layman I wondered if anyone could help me navigate what I'm looking at.

While I can orientate myself and visualise where we are in the milky way, what is the distinctive black band? I'm assuming it is caused by the absence of stars in these areas. However, as I understood it, the disc (as well as the center) are the areas of highest concentration of stars. Are these 'gaps' caused by dark matter?


texts: Does tidal heating imply orbit degradation?

texts: What compensate the energy loss in tidal heating? Is it orbital decay?


texts: Singularities/ringularities and their properties

texts:
A black hole contains a singularity at its center. It is a zero-dimensional point, and  it's where all its mass is located. So, my first question is:

If a singularity contains all a black hole's mass, when a black hole absorbs matter, the matter should collect at the singularity. Then why does the black hole increase in size? The matter it absorbs is all in the singularity, not in the space around it...

Second, we know that spinning black holes can't have a singularity at the center as a point, because points can't spin, and when they do, they aren't a point. So there is such thing as a ringularity where it is a one-dimensional line bent in a circle that spins, and contains all the black hole's matter.

However, is a ringularity really a bent one-dimensional line in a circle, or an infinite collection of points that form a circle-looking figure?

(My information on ringularities is from a paper published by Cornell University that compared the one-dimensional line to a bunch of zero-dimensional points, and videos by Kurgesagt.)


texts: Can this picture of the moon directly above the sun from the horizon be real?

texts: I recently saw this image, but somebody told me that it is fake, possibly photoshopped. The moon and the sun appear to be on the same perpendicular from the horizon. Is there any way to tell if this shot was actually captured?


texts: This is a very basic question but I am little confuse the difference between luminosity distance and distance. Can anyone tell me that what is the difference between luminosity distance and distance?


texts: Finding a location using the direction of shadow, UT and date approximately

texts:
Does anyone know how to find a location by using :

the direction of shadow relative to the normal (for example azimuth
angle)
the Universal time (UT) and date

I have a satellite image and I know north, time and date. One of the cues that I can use is, for example, in the northern hemisphere the direction of shadow is north.

Would anyone know if it were possible, and how, to calculate the location based on these parameters?


texts: Could you tell me this constellation name?

texts: Hi Everyone please check this pictures could you tell me this constellation name ?


texts: Why are relativistic jets perpendicular to the accretion disk?

texts: From looking at many images (artist's rendering and computer-generated) at black holes, I've noticed that the relativistic jets are always perpendicular to the accretion disk. Is this always true, and if so, why does it happen?


texts: Galactic rotation speeds - questions from a non-astronomer

texts:
Are there any observations that more distant galaxies appear to rotate more slowly than closer galaxies?
What methods are used to measure the rotational speed of galaxies? (both orbital speed profiles and/or bulk average rotation speed)
What is the current limit for how far away a galaxy can be to make such measurements?

I greatly appreciate any answer or links to info on this topic.  I am not an astronomer by profession or education, just deeply fascinated with cosmology.


texts: How much time does the ISS take to repeat its orbit?

texts:
I used to go to my roof to see the ISS, but it is not always visible. Then it appears again but does it appear with the exact same orbit as I saw before?
Thanks!


texts: We have discovered thousands of exoplanets so far. Do we categorize them into planets and dwarf planets, too?


texts: Peculiar Amplitude of Earth's Orbit in Z Axis

texts:
I'm currently building an N-body simulator for my masters project and I'm using JPL's Horizons system to compare against.

I started with just a couple orbits and everything seemed to be working nicely (After fixing many mistakes implementing a Fourth Order Integrator) but after extending to 10+ orbits I notice that in the Z-axis the Earth's amplitude increases linearly, according to JPL, but my simulation has a constant amplitude. JPL's result is shown in red in the bottom left:

What is causing this? Currently I only have the Sun, Earth, Moon and Jupiter in the system, but I didn't even realise the amplitude increased like this? What am I missing or got wrong?

(Also, the graph only shows 3 simulated orbits, and 80 JPL orbits)


texts:
There have been several accounts in media articles of asteroid near misses, many describe that the asteroid was not seen before the near miss.

After reading the question and answer to How can we tell if the asteroid 2013 TV135 will hit Earth in 2032?, where it was discussed about determining the orbits of known asteroids.

The question here is what is the furthest practical distance that a previously undetected asteroid, capable of an extinction level event, can be observed to have a trajectory that will result in a collision course with Earth?


texts: What is the fastest a galaxy or other body has been measured to (or can) travel?

texts: Our solar system travels at an average speed of 515,000 mph and our galaxy at 1.3 million mph through space. What is the fastest moving body in space recorded and the fastest can a black hole or galaxy travel through the universe?


texts: How can gravitational lensing makes a quasar appear brighter?

texts: How can gravitational lensing makes a quasar brighter than it would in the absence of a foreground galaxy?


texts: R.A. and DEC. for Constellation area vertices

texts:
I'm developing a planetarium software and I need the R.A. and DEC that represents every constellation area in the sky. I think I only need R.A. and DEC for each vertex.

Where can I find it?

I'm searching on Internet and I can't find it. Maybe because I'm not doing the right search.


texts: How many times brighter would full-earth-shine appear to people standing on the moon, than full-moon-shine does to people on earth?

texts:
The definition of brightness, according to Wikipedia:

the term brightness in astronomy is generally used to refer to an object's apparent brightness: that is, how bright an object appears to an observer. Apparent brightness depends on both the luminosity of the object and the distance between the object and observer, and also on any absorption of light along the path from object to observer.

How many times brighter is full-earth-shine as seen from the moon's surface, than full-moon-shine as seen from the earth's surface?
Different internet sources give different figures. I have seen figures as low as  3x (here), and as high as 100x (here). What is the right figure?
1st reference to be found In the last paragraph of the article.
2nd reference to be found on page 26.
Ethan on this website claims that the figure is 43x.
Besides an original answer, it would be good to get explanations on where the references made wrong calculations to get to their different conclusions.


texts: How to convert Proper Motion in RA & Dec to Galactic Coordinates

texts:
I'm trying to parse stellar data in the GAIA 2 release to galactic coordinates and am struggling with the velocity component. I've tried following online documentation and papers, but end up with velocity results with strange biases that indicate I'm probably doing something wrong. Sources I've used are:
http://adsabs.harvard.edu/full/1987AJ.....93..864J
https://gea.esac.esa.int/archive/documentation//GDR1/Data_processing/chap_cu3ast/sec_cu3ast_intro.html#SS
The GAIA 2 dataset has these relevant variables per star:

ra   (from 0-360)
dec  (from -90 to 90)
pmra
pmdec
parallax
radial_velocity

And this is the code I have (C#) to try to obtain the velocity components. Done by first converting pmra and pmdec to cartesian velocities based on the stars position, and then rotating that location to galactic coordinates.
double RA = ra * Math.PI / 180.0;
double DEC = (dec + 90) * Math.PI / 90.0;

Microsoft.Xna.Framework.Matrix positionrotation = new Microsoft.Xna.Framework.Matrix();
positionrotation.M11 = (float)(Math.Cos(RA) * Math.Cos(DEC));
positionrotation.M12 = (float)-Math.Sin(RA);
positionrotation.M13 = (float)-(Math.Cos(RA) * Math.Sin(DEC));

positionrotation.M21 = (float)(Math.Sin(RA) * Math.Cos(DEC));
positionrotation.M22 = (float)Math.Cos(RA);
positionrotation.M23 = (float)-(Math.Sin(RA) * Math.Sin(DEC));

positionrotation.M31 = (float)(Math.Sin(DEC));
positionrotation.M32 = 0;
positionrotation.M33 = (float)(Math.Cos(DEC));

Microsoft.Xna.Framework.Vector3 vector = new Microsoft.Xna.Framework.Vector3((float)(radial_velocity), (float)(pmra / parallax), (float)(pmdec/ parallax));
vector = Microsoft.Xna.Framework.Vector3.Transform(vector, positionrotation);

Microsoft.Xna.Framework.Matrix galacticrotation = new Microsoft.Xna.Framework.Matrix();
galacticrotation.M11 = -0.054876f;
galacticrotation.M12 = -0.87347f;
galacticrotation.M13 = -0.483835f;
galacticrotation.M21 = 0.494109f;
galacticrotation.M22 = -0.444830f;
galacticrotation.M23 = 0.746982f;
galacticrotation.M31 = -0.867666f;
galacticrotation.M32 = -0.198076f;
galacticrotation.M33 = 0.455984f;
vector = Microsoft.Xna.Framework.Vector3.Transform(vector, galacticrotation);


texts: Why didn't we see those campfires on the Sun until now?

texts:
What is it about its optics and instrumentation (aperture, sensors, filters), being in space and distance from the Sun on 30 May 2020 that allowed Solar Orbiter's HRIEUV telescope to see something that's never been seen before?
SOHO has been looking at the Sun in all kinds of wavelengths for a long time, and there's STEREO as well, and we've been looking at the Sun from high altitude balloons and sub-orbital rockets for over a half-century!
What could be the cause of solar "campfires"? provides links to a lot of information about the observed phenomenon, and eoPortal's Solar Orbiter Mission includes a lot of details on instrumentation .


texts: Why does it take so long to transmit an image from New Horizons to Earth?

texts:
I just got the news that the New Horizons space probe has passed by some remote planet on the edge of the solar system.

I was surprised that the guy from NASA says that it might take 24 months from us to get the photo of that planet.

The solar system is not that big, right? It is slow because the signal transmission is slow, right? But why is the transmission so slow?


texts: When was the last time a great conjunction coincided with a solstice?

texts:
This December, a great conjunction will occur nine hours after winter solstice, which means that for much of the world the two events will be on the same day. When was the last time a great conjunction occurred within 24 hours of a solstice?
As a rough estimate, consider that there are 96 hours per year that are within 24 hours of a solstice. So you'd expect about 1% of great conjunctions to be within this window. Given that great conjunctions happen once every 20 years, a great conjunction and a solstice should occur within 24 hours about once every 2000 years.


texts: Where can I find the positions of the planets, stars, moons, artificial satellites, etc. and visualize them?

texts:
What resources are available to find the positions of planets, stars,
moons, artificial satellites, asteroids, and other heavenly bodies?


texts: Could this be a cosmic ray hit on my cameras sensor (CMOS, DSLR)?

texts:
While taking pictures of the bubble nebula I noticed a very strange artifact on only one of my pictures. It can't be a satellite since its not a straight line and this is a 90s exposure that should make a line much longer. Also I doubt this is just readout noise from the camera (image is unstretched, unedited) since hot pixels don't form lines. So could this be a cosmic ray hit? If not does anyone have an idea what this could be?

The image was taken with my Canon 7D Mark II @ISO1600, 90s exposure.
Celestron C8 SGT (XLT), Celestron Advanced VX


texts: Why does time get slow near a black hole?

texts: Why exactly does time get slow around a black hole? And does it provide a way to go into the future?


texts:
Most of the news about extraterrestrial search focuses on possibility for existence of water and temperatures like earth. Why do scientists feel this would lead them to extraterrestrial life?

After all, we are searching for something that doesn't exist on earth. Why do we assume it would have behavior like us? Maybe the matrix inside their cells is of acetone or something else. Water may not play the role in their lives as it does for us. Maybe they can sustain high temperatures, maybe they can live in extreme cold. Why should we look for earth-like planets, isn't there a baseless (of course it's not baseless, there must be some logic which I want to know) assumption that the aliens are human-like (or any species on earth)?


texts: How are the elevations of the poles proportionate to distances of earth that have been traversed according to Copernicus

texts:
In chapter 2 of "The Revolutions of the Heavenly Spheres" where Copernicus maintains that the Earth is spherical, the Edward Rosen translation of the book states that

  the elevations of the poles have the same ratio everywhere to the portions of the earth that have been traversed.

I'd like to know what Copernicus is referring to in the aforementioned piece of text and how it provides evidence for the spherical shape of the Earth.


texts: Correct relation between metallicity (z) and iron content ([Fe/H])

texts:
The Wikipedia entry on Metallicity states that:

$\log_{10}\left(\frac{Z/X}{Z_\mathrm{sun}/X_\mathrm{sun}}\right) = [\mathrm{M}/\mathrm{H}]$
where $[M/H]$ is the star's total metal abundance (i.e. all elements heavier than helium) defined as a more general expression than the one for [Fe/H]:
$[\mathrm{M}/\mathrm{H}] = \log_{10}{\left(\frac{N_{\mathrm{M}}}{N_{\mathrm{H}}}\right)_\mathrm{star}} - \log_{10}{\left(\frac{N_{\mathrm{M}}}{N_{\mathrm{H}}}\right)_\mathrm{sun}}$
The iron abundance and the total metal abundance are often assumed to be related through a constant A as [citation needed]:
$[\mathrm{M}/\mathrm{H}] = A\times[\mathrm{Fe}/\mathrm{H}]$
where $A$ assumes values between 0.9 and 1. Using the formulas presented above, the relation between $Z$ and [Fe/H] can finally be written as:
$\log_{10}\left(\frac{Z/X}{Z_\mathrm{sun}/X_\mathrm{sun}}\right) = A\times[\mathrm{Fe}/\mathrm{H}]$

This all sounds reasonable, but I have two questions:

Where does the $[\mathrm{M}/\mathrm{H}] = A\times[\mathrm{Fe}/\mathrm{H}]$ relation come from? I could not find a proper source.
This article actually says (see Eq 9) that the general relation is $\log_{10}\left(\frac{Z/X}{Z_\mathrm{sun}/X_\mathrm{sun}}\right) = [\mathrm{Fe}/\mathrm{H}]$ i.e., they seem to equate [M/H] with [Fe/H]. I assume that it is because the aforementioned A parameter is between 0.9 and 1, but again that leaves me with the need for a proper source to state that.


texts: What would happen if a Black Hole and White Hole Collided?

texts:
Given our understanding of both black holes and white holes, what would be the outcome if they were both to suddenly collide?

Black Holes:

  A black hole is a region of spacetime from which gravity prevents
  anything, including light, from escaping. The theory of general
  relativity predicts that a sufficiently compact mass will deform
  spacetime to form a black hole. The boundary of the region from which
  no escape is possible is called the event horizon.

White Holes:

  In general relativity, a white hole is a hypothetical region of
  spacetime which cannot be entered from the outside, although matter
  and light can escape from it.


texts: With the expansion of the universe is time also increasing?

texts: With more space being created would there be more time in that new region formed? Is the over all universe increasing in time? This is my first question so go easy on me. PS. Would that also mean that the kinetic energy of the universe is increasing? If not what am I missing?


texts: Isn't Titan better to colonize than Mars? It has a thick atmosphere which is made up of nitrogen like our planet's. It doesn't have a magnetic field, but it does get a type of protection from Saturn. Maybe the only downside I see is that it is too far away. While Mars has neither a thick atmosphere nor a magnetic field, it is bombarded with solar radiation every day.


texts: Would drinking melted ice water from Mars taste like sparkling water?

texts:
Does water on Mars form from the atmosphere as ice free from salt?
Does water desalinize through the evaporation and transpiration?

When the fresh top ice is placed in a container then pressurized to melt, would the water be carbonated?

Particulates of salt and dust is less in the atmosphere during a Martian winter so would the ice that forms be also drinkably cleaner?

https://space.stackexchange.com/questions/33884/how-to-drink-water-on-mars
https://earthscience.stackexchange.com/questions/16076/how-salty-can-ice-be

https://kottke.org/18/12/a-massive-ice-filled-crater-on-mars


texts: These notes from an exoplanet talk discuss modeling the climate of exoplanets. How would we do that with our current technology? Would data be primarily gathered by spectrum analysis?


texts: Why isn't the moon's surface made of mini craters?

texts:
I thought that the millions of mini rocks that hit the moon would cause it to be entirely cratered and not flat.
Why is the moon not like this:

why aren't craters visible in the footprint photo?


texts: Does rotation affect gravitational lines of force

texts:
I was reading about rotating pulsars and other more-massive objects spinning at absurd speeds (hundreds of revolutions per second), and there was one point of which I was not clear.

Does a rotation of a mass change the gravitational lines of force? In other words, does a body which is rotating change the direction of gravitational pull from this:

to this?


texts: Are we made of the stuff of one star or more stars?

texts:
[T]his coincidence enabled stars in the late stages of their lives to turn helium into carbon, oxygen and most of the other atoms that you and I are made of. [...] [W]e're made of star stuff.

Max Tegmark, Our Mathematical Universe: My Quest for the Ultimate Nature of Reality, p. 64

Assuming that the Sun is not in the late stages of its life, I read that as that we are made mostly of star dust, but not Sun dust. Rather, we apparently are mostly made of atoms produced by earlier (now dead and buried) stars.

My question is whether it is likely that there was one immidiate (o.a. carbon-producing) predecessor star to the Solar System, or whether the Solar system likely has more than one (perhaps many) (o.a. carbon-producing) "parent stars"? (And, there seems to be also also a third "possibility": that the build-up of, say, carbon takes more than one generation of stars.) What's the (hi)story here?


texts: Best locations for large telescopes at high northern latitudes

texts:
Large optical telescopes want to be located at high altitude (get above as much of the atmosphere as possible). I get the impression that there is also a preference for low latitude (see as much of the sky as possible). And perhaps also for a location with good weather, so that there will be as few cloudy nights in the year as possible? So for example, many large optical telescopes are on the summit of Mauna Kea, Hawaii; there is also McDonald Observatory in Texas.

Suppose you wanted to put large optical telescopes as far north as possible, but still meet the other requirements, what would be a good location? Looking for high mountains at northern latitudes is an obvious starting point, but how well would that meet the requirement of clear skies? For example, Mount Washington in New Hampshire is the highest peak in the north-eastern United States, but has notoriously terrible weather; this would be an important downside?


texts:
Is there a formula to convert the B-V index to U-B index or are they totally different and separate observations and can't be convert like you can with Fahrenheit->Celsius?  (Updated)

I know F->C is not astronomy related directly but there is a formula to convert between the two measurements.


texts:
I'm wondering about the convention for keeping the calendar year in sync with the tropical (exact) year.  I did a preliminary calculation, but, it seems to be out by more than the average calendar year's additionally added leap second, every year or two.  Where have I gone wrong?  A bit of my reference material follows.
(365.2425 days/year - 365.24219 days/year) * (24 hours/day * 60 minutes/hour * 60 seconds/minute) = 26.7840000011347 seconds/year.  So, shouldn't this many seconds be subtracted, from the calendar year, each year?
Calendar year
The Gregorian calendar, as used for civil and scientific purposes, is an international standard. It is a solar calendar that is designed to maintain synchrony with the mean tropical year (Dobrzycki 1983, p. 123). It has a cycle of 400 years (146,097 days). Each cycle repeats the months, dates, and weekdays. The average year length is 146,097/400 = 365 97⁄400 = 365.2425 days per year, a close approximation to the mean tropical year of 365.2422 days (Seidelmann 1992, pp. 576–81).
Gregorian calendar
The Gregorian calendar attempts to cause the northward equinox to fall on or shortly before March 21 and hence it follows the northward equinox year, or tropical year. Because 97 out of 400 years are leap years, the mean length of the Gregorian calendar year is 365.2425 days; with a relative error below one ppm (8·10−7) relative to the current length of the mean tropical year (365.24219 days) and even closer to the current March equinox year of 365.242374 days that it aims to match. It is estimated that by the year 4000 CE, the northward equinox will fall back by one day in the Gregorian calendar, not because of this difference, but due to the slowing of the Earth's rotation and the associated lengthening of the day.
Leap seconds
Between 1972 and 2020, a leap second has been inserted about every 21 months, on average. However, the spacing is quite irregular and apparently increasing: there were no leap seconds in the six-year interval between January 1, 1999 and December 31, 2004, but there were nine leap seconds in the eight years 1972–1979.


texts: Exactly how long does it take for the exposed core of a star to cool from its starting temperature (several billion K) to ~50,000 K?

texts: OK, I didn't know how I should word this question. But the basic point is that most white dwarfs that we have classified fall in temperature ranges from ~50,000 K to 6000 K. However, at the end of a low-mass star's life, the core temperatures reach billions or maybe even trillions of Kelvin. So when the star dies and sheds its outer layers, exposing the core, exactly how long does it take for the core to cool down to the "standard white dwarf temperature?"


texts: Doing Correct Calculations with Binary Star Systems

texts:
I've been experimenting with Binary Star System calculations but came across some issues.

I can correctly calculate the Semi-Major Axis of the Earth's orbit around the Sun by doing the equation:

Using data from Wikipedia.

a = (1.521e11 + 1.47095e11) / 2.   <- average radius of Earth's orbit (meters)
μ = G * M = 6.67408e(-11) * 1.98847e30 gravitational constant * Mass of Sun (kg)

I got ≈ 31557884 seconds which equates to ≈ a year

Now my issue is that I've been searching around for a formula that calculates the period and etc of a Binary System where two masses (such as stars) orbit around each other.

So then I try essentially the same formula, this:

I used data from the Procyon A and B (binary system)

a = Semi-Major Axis = 4.3 AU
M1 = Procyon A Mass = 1.499 Solar Masses
M2 = Procyon B Mass = 0.602 Solar Masses

these give me a T (period) of 4731227. It says 40.82 years on Wiki.

What am I doing wrong? Is it the data? is it the formula? My comprehension of the question? Thank you for the help!


texts: Is it possible neutron stars are actual elements?

texts: As you go up the periodic table (more protons), the ratio of neutrons to protons steadily increases as well. Are we sure there are absolutely no protons and electrons in a neutron star, or could there be so much more neutrons that we cannot measure any protons and electrons? Perhaps then a neutron star is a nucleus of some huge element with a neutron:proton ratio higher than we can distinguish.


texts: How to calculate a planet's current position within the solar system

texts:
I'm making an application that needs to calculate a planet's current position within the solar system - I don't want to calculate its position in the sky.

For example, what I want to do is exactly what this website does:

http://www.theplanetstoday.com/

I want to create an overhead view of all the planet's positions in the solar system.

Where do I start? Is there a latitude/longitude coordinate system for the solar system? Everything I've found seems to calculate a planet's position in the sky from the observer's point on earth.


texts: What is the physical interpretation of the derivative of the emitted and observed wavelength?

texts:
The flux F of an event at redshift $z$ is related to its luminosity L as
$$F=\dfrac{L}{4\pi d_L^2}\,,$$
where $d_L\equiv d_L(z)$ is the luminosity distance between us (the observer) and the event (the emitter).

We also know that a photon emitted at a wavelength $\lambda_{em}$ is observed at
$$\lambda_{obs}=(1+z)\lambda_{em}\,.$$

We might want to know how does the observed spectra of the event $f_{\lambda}$ is related to the spectral energy distribution (SED) of the source $l_{\lambda}$. We can then deduce that
$$\dfrac{dF}{d\lambda_{obs}}=\dfrac{1}{4\pi d_L^2}\dfrac{dL}{d\lambda_{obs}}=\dfrac{1}{4\pi d_L^2}\dfrac{dL}{d\lambda_{em}}\dfrac{d\lambda_{em}}{d\lambda_{obs}}$$
$$f_{\lambda}(\lambda)=\dfrac{1}{4\pi d_L^2}l_{\lambda}\left(\dfrac{\lambda}{1+z}\right)\dfrac{1}{1+z}$$
$$f_{\lambda}(\lambda)=\dfrac{1}{4\pi d_L^2 (1+z)}l_{\lambda}\left(\dfrac{\lambda}{1+z}\right)$$

Although I understand that the factor $(1+z)^{-1}$ comes from the change of variable between emitted and observed wavelength, what is the physical meaning of it?
As an example, the $d_L^{-2}\propto (1+z)^{-2}$ and those two factors arises from the photons losing energy because of its wavelength being stretched and arriving further apart because the space between them grew.


texts: Can an average person see stars from the bottom of a well or through cardboard tubes? Definitive answer required!

texts:
A debate about seeing stars or planet during the day below this answer to the Aviation SE question At what altitude might a pilot be able to see at least the brightest stars during the day? seems unresolved.
I'm pretty confident that Venus can be seen during the day through a cardboard tube only because I've seen this mentioned so many times.
But what about stars? And what's this about Aristotle and Sir John Herschel?

Here's a reprint of the debate referenced above just in case some get deleted in the future:

Yes, but the thing with the hole is a hoax, that doesn't work. What does work are binoculars.

Tell it to Aristotle and Sir John Herschel (see edit above).

The link does not confirm the ability to see stars from the bottom of a shaft, but rather refutes it.

Since they failed, even with binoculars, one wonders if sky conditions were less than optimal (a cirrus layer that isn't even readily visible would broaden the point of a star enough to make it invisible against the general scatter). Star visibility from the ground in daylight is well documented and repeatable, and doesn't require visual aids, if only the sky is completely clear.


texts: Is it possible to see a moonrise or moonset twice in a day?

texts: I've been wondering this for quite some time.  Due to the variations in tilt from the earth we know that moonrise/moonset times vary.  Is it possible that in any location on the earth one might see more than one moonrise or moonset in a given 24 hour period?


texts: What of the following moon-situations would be better?

texts:
Okay, so imagine that there is an Earth-like planet, with the following conditions:

It's further from it's sun than the Earth is from the Sun (not much, but enough for weather to be a little colder than the Earth).
It's more or less the same size as the Earth (same proportion of land and water, too).
Since it's further from it's sun, it takes more time to complete an orbit that the Earth (for instance, 400 Earth-days, instead of 365).

Given those conditions, I would like to know which of the following would be more stable for this Earth-like planet to have a similar day/night and moon cycle to the Earth:

A moon that's the same size as the Earth's moon, only closer.

OR

A moon that's as far away as the Moon is to Earth, only that the moon of this planet is bigger (let's say, twice as big as our moon).

Sorry if it's kind of complicated. Please tell me if it's not understandable and I'll try to edit it so it's as clearly as possible!
Thanks in advance :)


texts:
I wrote an experiment in HTML5 and Javascript to try to show what is happening to the curvature of spacetime as a body moves through a region.

As time progresses, I'm using the g=Gm/r2 equation to move the spacetime grid toward the object. When a grid point is within the body, I use g(1-h/R) to modify the bending according to the acceleration at the surface. This assumes uniform density.

The result is that it takes a very large mass and very long time for any sort of noticeable curvature to occur (as you'd expect). By decreasing the Earth's radius by a factor of 3, I was able to see the curvature very well as in the screenshot below.

What occurred to me then is that the the warping of space would remain long after the body of mass had moved on.

Does this warping in space ever return to truly "flat" or is the fact that we almost never orbit through the same absolute region of space mean we never experience this existing warping?

If light went through this "wake" would it bend according to the spacetime curvature created by the long distant planet? Or have I gone wrong in my model?

This demo uses real values except that the radius is shrunk by 3x to increase its gravitation effect.

earth.radius = 6.371e6 / 3;
earth.mass = 5.972e24;
spacetimeGrid.extent = 4.5e7;

You can run the demo here: https://dl.dropboxusercontent.com/u/2236585/spacetime/index.html


texts: What are the masses of the two stars (given the information provided)?

texts:
If anyone would at least be willing to point me in the direction of finding the answer, or help me solve it I'd appreciate it. I don't know how to go about this, and need to know how to solve this on my own (plus I need the answer for a homework assignment, but just an answer isn't gonna help).

Question:

The spectral lines of two stars in a particular eclipsing binary system shift back and forth with a period of 10 months. The lines of both stars shift by equal amounts, and the amount of the Doppler shift indicates that each star has an orbital speed of $~8.0\cdot 10^4~ \mbox{m}/\mbox{s}.$
What are the masses of the two stars? Assume that each of the two stars traces a circular orbit around their center of mass.


texts: How does radio bandwidth restrict the choice and use of science payload on interplanetary probes?

texts:
I asked a question here about returning to Earth a physical memory capsule along with soil samples, as a complement to radio operations as today. This might return a much larger amount of data compared with radio today, but of course only at the end of the mission.

How useful would it be for a sample return mission like Mars2020 or Hayabusa2, to be able to return much more data? Would the choice of instruments change to allow for higher sampling rates, higher resolution, more filters et cetera? Is Big Data science instruments from an interplanetary mission even a possibility, or is today's bandwidth good enough for any conceivable payload?


texts:
I want to do project on astronomical dataset. Regarding that project, I try SDSS who give public dataset but it is quite complicated for me. I gone through public dataset and downloaded some .FITS file one is ~3.2mb and other one is ~3 GB but I don't know how to deal with this file and generate images or other files from .FITS files.

Please help me, this is my Master's project in computer science.


texts: Any cheap (less than 100 euro) telescope for observing Jupiter?

texts:
The moon is not challenging.

I would like to observe the big planets and their rings.


texts: Dark enough to see stars during total solar eclipse?

texts:
I was fortunate enough to see totality during the eclipse of 2017 August 21.
It did leave me wondering about the 1919 Eddington experiment, though.  During totality, it only got dark enough to see a few of the brightest objects like Venus and Jupiter.  It was more like twilight than night that way.

So how were they able to see and photograph stars in the 1919 eclipse?  Do skies get darker during some total eclipses than others?  Was there more light scattering in my case, from being in a populated area?  Or do the right optics let you photograph stars during twilight-like conditions?


texts: Have there been any confirmed PISN supernovae?

texts: I did some research on pair-instability supernovae (PISN), and wondered if there have been any confirmed superluminous supernovae caused by a pair-instability. Are there any confirmed PISNs out there, and if so, which one(s)? If not, why is it so difficult to detect and/or confirm these rare events?


texts:
From certain positions in outer space the Earth will appear to have a blue ring around it when the viewer is in the shadow of the Earth and sunlight is passing through the atmosphere.

Here is a simulation from Google Earth:

Sample sentence: The astronaut looked down at the blue ring formed by the sunlight passing through the atmosphere around the Earth.

Is there a word that describes this ring?

I had assumed the ring would be blue, based on this photograph from the Tumblr site Col. Chris Hadfield:


texts: What is the smallest possible planet with same sea level atmospheric pressure as Earth?

texts:
Suppose there is a planet made of pure tungsten (a quite common and heavy element), with perfect spherical shape.

Which should be its radius so that the air pressure and ground/sea level is the same as on earth ?

I don't know if it is sufficient to have a 1G gravity, because the smaller radius could affect the density of the atmosphere as the gravity will decrease differently that from earth.

For sake of simplificy, say that this planet is on the same orbit as Earth, orbiting around a twin of our Sun. Also magnetic field and atmosphere composition should be comparable to the Earth's one (altough this is not realistic, due to the lack of body of waters).


texts: I have a template spectral energy distribution (SED) at z=0. I want to shift the template SED to an arbitrary redshift (z>0), how to do this in python?


texts: How often do comets survive passage by the Sun?

texts: I had heard that comet ISON might not survive a close pass by our Sun, and I was curious about the odds of how other comets had fared. So, how often do other comets survive a close pass by our sun? Also, are there any connections between a comet's size or buildup(of material) that makes it more or less likely to not survive?


texts: Sun, Moon: Relative Distance from Crescent?

texts:
This is more a question about the history of astronomy.

It recently occurred to me that you can estimate the ratio of earth-moon and earth-sun distance in the following way: We can look at the triangle observer-moon-sun. Call the angle at the observer $\alpha$, the angle at the moon $\beta$.

At the crescent to half moon stage, sun and moon are both visible, so one can determine the angle $\alpha$ (at the observer).
From the illuminated fraction of the moon, one can estimate $\beta$. (Precision is presumably lower here.)
Thus, the third angle is fixed, and the shape of the triangle is known (but not the overall scale).

So it should be possible to derive that the sun is much further away than the moon. If we could get an independent determination of, say,  the earth-moon distance, the distance to the sun would be known.

This seems rather straightforward. Has this been used historically? What accuracy was (could have been) achieved? For example, I seem to recall that in the "celestial spheres" approach, people have at least ordered the heavenly bodies according to distance, but has this method been taken into account?


texts: Do objects that are invisible to the naked eye occlude much of the stars to Earth based observers?

texts:
I was looking at a star recently and some other object that appeared to be stationary in relation to the star was occluding the light to only one of my eyes. This is why it caught my attention.

I was able to move my head around this shadow and see the star but there was a definite tiny area where the star was clearly hidden. The object hiding the star also appeared to be a similar size to the tiny point of light of the star. Is this common to observe?

For the last few days I have been asking myself how many objects could be hidden like this (though most with shadows that engulf the earth); How thick are asteroid belts etc, that are between our eyes and the rest of the stars.

Is most of it hidden?


texts: Did cosmological inflation occur at speeds greater than $c$?

texts:
If cosmological inflation occurred at speeds less than $c$, wouldn't we see the CMB right in front of our noses (or not at all) instead of at 13.7 billion light years?
And if it happened faster than $c$, does that mean inflation occurred before the current laws of physics (read the four basic forces) precipitated, was $c$ greater then than it is now?


texts: Exoplanets, Protoplanets, and planetesimals

texts:
So, most of the mass of the solar system (that isn't inside the sun) is inside Jupiter. And most of whats left after THAT is inside Saturn. So, all the rocky planets, moons, and asteroids in our solar system are a tiny minority of the mass.

Now, we're looking at other solar systems for Exoplanets, and mostly finding gas giants. But not every system has one that we can detect- even some of the nearby systems. Which implies that there are plenty of systems without a Gas Giant.

Unless I'm misunderstanding things, the amount of raw material in those systems should be fairly similar to ours. So what, realistically, would those systems have in terms of planets? Without the massive gas giants to suck up all the mass, they'd presumably have lots of smaller objects, right? Massive asteroid belts, large numbers of small planetoids? Are there any models of what those systems are likely to look like?


texts: INDI protocol with AZ GoTo SynScan to control an amateur telescope mount : problem with tracking

texts:
I have a SkyWatcher telescope with an AZ mount and a SynScan GoTo to drive the telescope.

I want to drive the telescope from my computer.
Using Linux, I use the INDI protocol (https://www.indilib.org)  with the Kstars/Ekos software.

The problem is that, when I ask the system to track a specific RA/DEC coordinates point, the telescope slews but then stops tracking.
I have the same problem using carte du ciel instead of Kstars.

Here are some system specifications

synscan version : 4.39.1
indilib version : 1.8.3
OS : Linux Debian 9

Has it happened to someone else?


texts: How tall are the "fractured" linear structures on Europa's surface?

texts:
What are the altitude differences in the high resolution part of this image of Europa?

How high do those ridges rise over their neighboring valleys? And how large is the area shown in this image?

And are the craters believed to have been formed by impacts or some kind of "eruptions" from below? It looks to me as if the areas which have the most (tiny) craters is on top of and thus newer than the less cratered areas. Well, here and there anyway.


texts:
Well, I'll start off by saying I am certain I am doing it wrong! Now that I got that out of the way here is my image:

I have a feeling I can't see the planet because I need a filter to block out the light surrounding Jupiter, however I honestly didn't expect to have such a profound atmosphere-like disc around Jupiter.

My fiance thought it was my own eye being projected, but it was a DSLR doing the actual looking.

I am using the Celestron NexStar 127 SLT which comes stock with a 25mm and 9mm eyepiece.

Update:
Okay! I focused and was able to see Jupiter, including some aspects of its atmosphere. However, I was not able to take a descent picture of it. Now I'm thinking the need for filters and proper DSLR usage methods will come into play.


texts: Active Galactic Nuclei - categorisation on the basis of observer?

texts: As we know AGNs are considered to be one of the most luminous objects to be found in the cosmos.Based on the observer, for instance on Earth,  we categorize them on the basis of the angle between the observer and the object. Suppose for instance there are two observers, one on Earth and one on some distant planet (far away from our solar system,  let it be on the opposite side of the Milky Way relative to us). Would both the observers relate an AGN belonging to the same class? In other words, can these categories be relative to their viewing? Like an object can be a QSO to us but to the other observer can the same object be a Seyfert or a Blazar or an RG?


texts: Is there any benefit to view the 3D (real) universe as 3D projective space?


texts:
I currently own a telescope, I'm an amateur astronomer and currently just trying to view the moon. I own the Celestron PowerSeeker 70AZ.

Link for information on the telescope: http://www.celestron.com/browse-shop/astronomy/telescopes/powerseeker-70az-telescope

The problem: I can't view the moon! All I see is a big ball of white, and since I'm new I thought I could get some advice for eyepieces:  mine being a regular 20mm eyepiece. I don't use a barlow lens, mine broke.

Thanks! If you want any more specifications, just ask. I'm just looking for help! Thanks!


texts: Can moon set after being up when due north? (pseudo circumpolarity)

texts:
I'm in the northern hemisphere, facing north, and notice that the moon
is due north (azimuth 0) and is still above the horizon, albeit barely.

Does this mean the moon is necessarily circumpolar (doesn't set), at
least for the next few hours?

As the moon moves away from due north, it's altitude/elevation
normally increases. However, it's possible that the moon's declination
is decreasing so rapidly that the moon's elevation actually decreases,
and the moon sets.

Is this possible?

This question is tangentially related to my question "libnova odd behavior for 89.5 degrees north latitude" on Stack Overflow.

EDIT to answer questions: I am facing true north. I am referring to the Earth's true moon, but not necessarily in any given time frame. In other words, if something like this happens 10,000 years from now, that's fine.

EDIT: OK, I believe the moon CAN set even if it's up when due north. Example:

You are at latitude 89.5N
The moon's declination when due north is +0.5N. This means the
moon grazes the horizon when due north.
If the moon's declination were constant, it's highest elevation
for the day would be 1 degree.
Since the moon's declination can change more than one degree per
day (average of 1.5 degrees/day), it's quite possible for the moon's
declination to go below -0.5N, at which point it would have set (it
will actually set before this point unless it happens to reach due
south).

In theory, this could happen with any object whose declination
changes, provide you're close enough to the North Pole.

I'll leave this update open for critiques.

EDIT: Actually, this whole question is just asking whether the midnight sun/moon can set at any position other than due north, which is fairly obviously true. Reasoning: once the moon/sun finally sets not due north, it was obviously still up the last time it was due north.


texts: Is the Ordovician meteor event detectable in the lunar cratering record?

texts:
Approximately 468 million years ago there were a large number of L-chondrite meteorites falling to Earth. This is called the Ordovician meteor event and was probably the result of a large collision in the asteroid belt.

Does the lunar cratering record also show evidence of this event?


texts: If Venus had moon before and it fell back to Venus, why don't I see a unique, very big crater?

texts:
Does lack of a very big crater support the idea that Venus never had big moons before?

If not, why can't I find a very big crater from the moon impact?


texts:
I've been trying to install MOOG Nov2019 (utexas, Wiki) on my desktop running OpenSUSE 13.1. I have the SM and X11 library paths copied into the makefile, and I am 3-sigma confident that they are the correct pathways. I'm using cc as the C compiler, and gfortan for Fortran. When I run the makefile, I get a string of errors that looks like this:
gfortran -Wall -g -std=legacy Abfind.o Abpop.o Abunplot.o Batom.o Begin.o Binary.o Binplot.o Binplotprep.o Blankstring.o Blends.o Bmolec.o Boxit.o Calmod.o Cdcalc.o Chabund.o Cog.o Cogplot.o Cogsyn.o Correl.o Crosscorr.o Curve.o Damping.o Defcolor.o Discov.o Doflux.o Drawcurs.o Eqlib.o Ewfind.o Ewweighted.o Fakeline.o Findtic.o Finish.o Fluxplot.o Gammabark.o Getasci.o Getcount.o Getnum.o Getsyns.o Gridplo.o Gridsyn.o Infile.o Inlines.o Inmodel.o Invert.o Jexpint.o Lineinfo.o Lineabund.o Linlimit.o Makeplot.o Molquery.o Moog.o Mydriver.o Nansi.o Nearly.o Number.o Obshead.o Oneline.o Opaccouls.o OpacHelium.o OpacHydrogen.o Opacit.o Opacmetals.o Opacscat.o Params.o Partfn.o Partnew.o Plotit.o Plotremember.o Pltabun.o Pltcog.o Pltflux.o Pltspec.o Pointcurs.o Prinfo.o Putasci.o Readobs.o Rinteg.o Setmols.o Smooth.o Specplot.o Stats.o Sunder.o Synpop.o Synspec.o Synth.o Tablepop.o Taukap.o Total.o Trudamp.o Ucalc.o Vargauss.o Vmacro.o Voigt.o Wavecalc.o Weedout.o Writenumber.o -o MOOG -L/usr/local/lib/X11  -lX11 \
        -L/usr/local/pkg/sm/2.4.36-F90/lib -lplotsub -ldevices -lutils

Abunplot.o: In function `abunplot_':
Abunplot.f:(.text+0x624): undefined reference to `sm_defvar__'
Abunplot.f:(.text+0x64e): undefined reference to `sm_window__'
Abunplot.f:(.text+0x66c): undefined reference to `sm_limits__'
Abunplot.f:(.text+0x6c6): undefined reference to `sm_ticksize__'
.
.
.

Running the nm command in the sm library yields:
> nm /usr/local/pkg/sm/2.4.36-F90/lib/libplotsub.a | grep ylabel
0000000000001cc6 T sm_ylabel
                 U sm_ylabel
0000000000000dae T sm_ylabel_
                 U sm_ylabel

Based on the readme for MOOGStokes (https://www2.mpia-hd.mpg.de/homes/deen/Software/MoogStokes/MoogStokes.README.txt), it looks like this error arises from how gfortran and SM handle underscores. I've tried using the gfortran flags listed in the MOOGStokes readme, but the problem persists. Are there other flags I should use, or is there another way to resolve this?


texts: How did New Horizons take such well-lit pictures of Pluto?

texts:
The photos of Pluto from New Horizons are truly beautiful.

But considering that Pluto is so far away from its nearest start - our Sun - how is it so well lit up?

Did the New Horizons have a massive flash mounted on its camera to illuminate the planet or is there just a lot of ambient light in space?

I'm really curious.


texts: How fast would we have to go for the red(/blue)shifts of galaxies ahead of us to differ from those behind us with statistical significance?

texts: Here, we are looking for a statistically significant difference between the mean redshifts of galaxies ahead and those behind, with reference to a prior-specified direction. For example, suppose that we were aboard an advanced spaceship that had been accelerating in that direction at (say) 1 $g$ for some years. How soon into our journey would we notice that the galaxies ahead were bluer than the galaxies behind? Clearly this depends on our existing model, based on prior observations, for the distribution of galaxies' redshifts, and on some reasonable kind of weighting for each individual galaxy (perhaps according to the cosine of angle from our direction of travel, but not according to the galaxy's distance). However, in this analysis, we are ignoring individual data about any particular galaxy acquired before our present observation. For simplicity, let us also suppose that there is no statistically significant difference between the mean redshifts forward and back in the line of our journey before we began it. For the sake of definiteness, if it is needed, let us take a significance level of 1%.


texts: How do I deduce my latitude and longitude from N obervations of occultations from the same place?

texts:
I think it would be an interesting exercise to measure the latiude and longitude of my house using N occultation timings. I would like to see how precisely I can measure it using that technique, and compare it with the GPS readings from my phone.

I'm looking for a reference which will tell me how to do the calculation of inferring my position from occultation timings, as accurately as possible.


texts: Simple question, but can't seem to find the answer anywhere. It can't be nuclear fusion because nuclear fusion occurs as a result of the heat. And it can't be because of gravity because it's believed that the core of black holes are nearly absolute zero. So what makes stars hot?


texts: Per the Big Bang Theory, the universe was formed from a dense singular point which existed 13 billion years ago and has been expanding ever since. This suggests that the point should have existed somewhere in space implying an outer universe. If we call this point the "Universe", then what do we call the space that held that point? Also how did this single point come into existence in the first place?


texts: How common are exoplanets in distant orbits?

texts: Are there many single transits in the Kepler data, which might be exoplanets with a longer orbital period than the time they have been observed for transits? Can any conclusions be drawn about how common they are? Is there reason to believe that the outer solar system is a common configuration? I suppose that slow moving planets are hard to detect also with doppler measurements. Will the upcoming telescopes aimed at nearby stars be able to find 10+ AU orbital radius planets?


texts: By how much does Haumea's fast rotation affect its surface gravity?

texts: The equation for surface gravity is $\frac{GM}{r^2}$ but I'm not sure how to include the effects from its rotation.


texts: How is the field of view of a radio telescope determined?

texts: It’s my understanding that radio telescopes can only receive signals that hit the dish within a certain range of angles. How is that angular range determined i.e. measured and/or calculated?


texts: Reason for disqualifying Pluto as a Planet?

texts:
Pluto is no longer a member of the planets in the solar system.

Why was it disqualified as a planet?
What is the criteria for classifying an Astronomical Object as a Planet?
Does this criteria apply to all Star Systems or just our Solar System?


texts: Are there any stars that one day we could collide with?

texts: I'm not talking about tomorrow but in the far far future could we say our Sun could collide with another star or otherwise within our current detectable range?


texts: Reference: First spectrographic observations by Fraunhofer

texts:
In several books I find reported that the first scientist to perform spectrographic observations of celestial objects was Fraunhofer with the spectrographs he himself produced. I do not find though a reference, a paper, in which he presents this work.

Using the NASA astrophysics data systems I find only the papers concerning his technical work with glasses but not the observations of Venus, Mars, and other heavenly bodies, he performed.

I find books on Google Books reporting such observations
but unfortunately I can view limited parts of these books and not their bibliographies.

Anybody can find a reference for any of these observations?


texts: Can visible wavelength spectroscopy study an exoplanet's chemical composition directly?

texts:
I know spectroscopy of light in visible wavelengths is very effective for studying and determining the chemical composition of bodies within the solar system and bright objects outside of it. However, can this same method be used with exoplanets?

In looking about some related articles, I've learned that it is possible, if a planet passes between us and its star, to filter out the star's light leaving only what passes through the planet's atmosphere.
But what if there is no such occultation? Can we filter out the star's light in other wavelengths like UV or infrared and look at just the planet via its own emitted radiation (assuming the planet is large and hot as these are what we are most able to detect at this time)?


texts:
Looking at sunrise and sunset data around 2017 vernal equinox (because of GMT timezone I took London) https://www.timeanddate.com/sun/uk/london

Date  Sunrise      Sunset        Day Length  Solar Noon
16    06:12 (92°)  18:07 (269°)  11:54:55    12:09 (37.0°)
17    06:09 (91°)  18:08 (269°)  11:58:53    12:08 (37.4°)
18    06:07 (90°)  18:10 (270°)  12:02:52    12:08 (37.8°)
19    06:05 (90°)  18:12 (271°)  12:06:50    12:08 (38.2°)
20    06:03 (89°)  18:13 (271°)  12:10:48    12:07 (38.6°)
21    06:00 (88°)  18:15 (272°)  12:14:47    12:07 (39.0°)
22    05:58 (88°)  18:17 (273°)  12:18:45    12:07 (39.3°)

We see that 12-hours day happens around 17-18 of March, however the Vernal Equinox takes place on 20 March 2017, 10:29 GMT.

I understand that due to refraction in the Earth's atmosphere and due to the fact that sunrises and sunsets are defined by the top of the Sun's disk, sunrises are "earlier" and sunsets are "later", so the 12-hours day indeed should happen before the equinox.

But why the directions of sunrise and sunset are east--west on that same day? The above factors should not influence directions, should they?


texts:
Current answer(s) to How do telescopes "zoom" and change angle of view? are "they don't", but traditional large genera-purpose observatory telescopes do sometimes (often?) have multiple focuses with different f/ numbers.
I vaguely recall about 1 mya a 24 inch (0.61 meter) Boller and Chivens with a primary focus at the back for photographic plates, and a little door somewhere along the side of the telescope where you would reach in with one arm, feel your way around and somehow rotate something into place that would send the light path down though the mount into a big room on the floor below where a pair of grating spectrographs sat on concrete pedestals, a "normal" one and an Echelle, both with photographic plate holders.
During the procedure fiddling around inside the telescope, one had to be extremely cautious not to touch any optical surfaces; which at 3 AM in the dark it was quite a challenge.
Presumably this presented a far longer f/no. focus for the slits. We;d place the slit across Jupiter, develop the Echelele plate, and measure it's rotation rate on a Mann measuring machine if I remember correctly.
Question: How did I flip some mirrors around in the dark at 3 AM and change the focal length of a 24 inch Boller and Chivens?

Example of a similar instrument found on the internet: Eastern Iowa Observatory offers a chance to see the stars and so much more. The "mirror-swapping door" of which I speak is probably on the other side of the telescope.


texts: Is it possible to manipulate the size of a black hole or how a black hole behaves if scientists were able to synthesize hawking radiation on demand.  That is, if I could find a way to imitate hawking radiation in a missile would this missile decrease the size of the black hole I fire the missile at?  I am thinking provided I create enough hawking radiation it should have an effect on the black hole size once the missile detonates. That is if it is true that hawking radiation can make the black hole disappear as it does one the mini black holes who die because of hawking radiation.


texts: Could the Sun's magnetosphere block extraterrestrial contact?

texts: I was reading how certain strong magnetic fields can block or alter radio waves so bearing this in mind would it be possible for the Sun's magnetosphere to block attempts to establish radio contact from other solar systems if the signal is weak enough?


texts: Is there any plausible astronomical source of energy that could wipe out humanity without rendering the planet inhabitable?

texts:
I'm aware of hard radiations from space can wipe out life but I believe that would also causes the planet to be inhabitable for a period of time. Is there any other kind of energetic astronomical event that could destroy life through a transient pulse of radiation (particles or photons) without any "cool down" needed for new life to develop?

The event could be known or theoretical or just plausible that spans entire galaxy if necessary.


texts:
http://exoplanets.eu/ displays R.A. on screen in hh:mm:ss format but when you export the table, it gives the R.A. as a decimal.  Likewise for Declination.

How can I turn for example 24.35417 (WASP-18) into 01:37:25.0 ?  And likewise for Declination -45.67778 to -45:40:40?  I'm looking for a method, not a website that will do it for me.

Either a way to convert between formats or how do I export in non-decimal format?

Thanks


texts: Is the angular resolution of a telescope irrespective of used eye-piece?

texts:
Suppose a telescope has aperture $D = 20$ cm. The angular resolution of such telescope, according to the Rayleigh criterion (if I have understood it correctly), is given by

$$\theta = 1.22\cdot\frac{\lambda}{D} \text{ rad}$$

where $\lambda$ is the wavelength of light and $D$ is the aperture. Suppose $\lambda = 550$ nm (mid-point of visible light). Then

$$\theta = 1.22\cdot\frac{\lambda}{D} \text{ rad}
= 1.22\cdot\frac{550 \text{ nm}}{20\text{ cm}} \text{ rad}
= 1.22\cdot\frac{5.5\cdot10^{-5}\text{ cm}}{20\text{ cm}}\cdot 206264.8''
\approx 0.69''
$$

In other words, the angular resolution of the telescope is $0.69$ seconds of arc for $\lambda=550$ nm.

Now, is it really so that the eye-piece of the telescope has no play in this at all? Wikipedia says that

  and D is the diameter of the lens' aperture.

which I would understand to be taken as the size of the primary mirror alone in a Newtonian telescope.

So if there is for example a double (binary) star, I will see them as one no matter what kind of magnification/eye-piece I am using if the angle between the stars (from my point of view) is less than $0.69''$? And vice versa, if the angle between the stars is greater than $0.69''$ I will see them as separate stars with any eye-piece or magnification?

(In theory, I know there's a lot of limitations from optics, seeing, etc.)


texts: How strong are the stellar flares on YZ Ceti?

texts:
Doing research for a game and trying to understand the implications of the stellar flares from YZ Ceti. In short (ignoring the planets for now), if people were to build large space stations of various types (O'Neil cylinders, hollowed out asteroids, etc.), do the YZ Ceti flares pose a significant danger to them? If so, what would be the frequency and scale of such danger?

Better still, what reliable sources can I consult and how would I interpret them so I can figure this out on my own? I'm getting tired of searching and finding the Kerbal Space Program forums.


texts:
Recently I've become more interested in the topic of the stability of planetary systems. I have been reading about it and it seems that orbital resonances play an important role in the stability of Solar System (as well as in the moons of Jupiter and other planets).

I first thought that the orbital resonance is somehow more stable and thus we have several cases in the Solar System.

But as I kept reading, I found out that in the asteroid belt there were some gaps precisely where the resonances happen, so the resonances are actually instable for asteroids.

I then thought that some resonances are stable while others are instable, but some of the resonances that makes gaps in the asteroid belt are actually present in the Solar System between planets, so I am completely lost.

Why resonances are sometimes stable and sometimes instable? What am I missing?
Maybe I am misunderstanding something because it doesn't make sense to me. Any help will be welcome.


texts:
I'm trying to find/create a star map between the declinations of -45 to +60, and need it to be a rectangle. Is there any software/website that would let me create this? Is there a name for this kind of map/projection?

(I've attached a diagram to try and make myself clearer)

Thanks for any help :)


texts: What shape does a three dimensional universe have ? and how did scientists determined that it is flat and not curved.


texts: Accelerating universe expansion and standard candle

texts: Recent stars (and standard candle supernova), afaik, contain more heavy elements than older stars. As consequence, I guess, recent stars and supernova should be slightly dimmer than older stars? If previous sentence is true, slightly dimmer Ia supernova will appear as if it is more distant leading to the conclusion that universe is expanding faster. Does measuring of universe expansion rate and "dark energy" takes such possibility in to the computation?


texts: What could be the cause of solar "campfires"?

texts:
NASA/ESA Solar Orbiter mission just released its first images. They show an ubiquitous feature: miniature flares called "campfires", much smaller than solar flares.

(click to enlarge)

A high-resolution image from the Extreme Ultraviolet Imager (EUI) on ESA’s Solar Orbiter spacecraft, taken with the HRIEUV telescope on 30 May 2020. The circle in the lower left corner indicates the size of Earth for scale. The arrow points to one of the ubiquitous features of the solar surface, called ‘campfires’ and revealed for the first time by these images. © Solar Orbiter/EUI Team/ESA & NASA; CSL, IAS, MPS, PMOD/WRC, ROB, UCL/MSSL

ESA press release goes:

The scientists do not know yet whether the campfires are just tiny versions of big flares, or whether they are driven by different mechanisms. There are, however, already theories that these miniature flares could be contributing to one of the most mysterious phenomena on the Sun, the coronal heating.

NASA press release says:

It’s not yet clear what these campfires are or how they correspond to solar brightenings observed by other spacecraft. But it’s possible they are mini-explosions known as nanoflares – tiny but ubiquitous sparks theorized to help heat the Sun's outer atmosphere, or corona, to its temperature 300 times hotter than the solar surface.

So these campfires could be the cause of coronal heating, but what could be the cause of the campfires themselves? I understand that it might be a bit too early to ask this question, as these campfires have just been discovered, but I am eager to know if some people have theories about what could be going on.


texts: Does the image of the cosmic microwave background radiation show us what the universe used to look like?

texts:
Is it possible to interpolate using the cosmic microwave background radiation and currently what we can see in the sky at night to predict what the night sky will look like in the future? I’m guessing the night sky will be increasingly bright regardless of light pollution on earths because more light from galaxies will reach us in more time?  If we can interpolate forwards, would we be also to interpolate backwards?

From my understanding, the cosmic microwave background radiation is what the universe used to look like.


texts: Is there a natural process by which hydrogen is generated from heavier elements in the cosmos?

texts:
we know that stars fuse hydrogen into helium starting at 3 MK; 13 MK in the Sun's core;
carbon fusion starts at above 500 million K, and silicon fusion starts at over 2700 million K for comparison;
we know fusion stops at iron, because a star has to use more energy to fuse that than it gets back;
so heavier elements are created mostly in a supernova (but also possible in small quantities by special processes like neutron capture);
finally sun-like stars end up as white dwarfs, bigger stars as neutron stars, quark stars, black holes;
and black holes ultimately convert themselves into radiation, in the far distant future when the stable black hole mass limit goes up high enough that even the most massive black holes evaporate;

http://en.wikipedia.org/wiki/Vacuum_Diagrams

so my question is, will it be like Stephen Baxter said, that in the future only radiation will be left in the universe?
Specifically, is there a natural process out there by which hydrogen is spewed into the cosmos, converted back from heavier elements, to regenerate the fuel for stars so that they may shine in the far distant future as well?

Of course we don't need to worry about this for the time being. This is only considering our concern with what will be 10^70 years from now.


texts:
I wasn't around when man landed on the moon in 1969. When I see the moon, I always wonder, were people able to see the rocket?

Yesterday, I looked at the moon in daylight and wondered again.

My question is: how far were people able to see the rocket after it launched?


texts: Was the expansion of space time during big bang uniform if so how come the stars and planets be formed because and matter as well as gravity would have been same everywhere


texts: What is the apparent magnitude of the faintest stars visible during a full moon?

texts: Assuming the viewer is far from any light pollution, it is a cloudless night, and humidity is very low.  What is the faintest apparent magnitude of stars visible to the naked eye during a full moon (at zenith) if the viewer is looking towards the horizon?


texts: How long can you be trapped orbiting around a black hole for?

texts:
I have a story I wanna write but I want to be sure it's not completely scientifically irrelevant.

I know there is  black hole modelisation called the Kerr black holes, in which there is a limit around black holes called the event horizon. It's a spatial limit ; no light ray crossing this limit will ever be able to escape the gravity of the black hole. That's the definition of event horizon.

By extension, I guess any physical object (such as a spaceship) crossing the event horizon will be doomed to orbiting around the black hole until it gets destroyed. My question is about the time you can spend between the moment you cross the event horizon (= you are doomed) and the moment you actually die (for example by the tide effect, which basically destroys bodies because of the difference of attraction force between the feet and the head of a human body)? Could this moment last... 100 years ? 1000 years ?
(for my story the more the better)

I know black holes studies are very theoretical, I'd just like to avoid any huge scientific plot holes.

I am quite unskilled in that domain of astronomy, about time dilatation, etc. So if anyone has any idea of the order of magnitude of the time a object can spend beyond a black hole event horizon before it gets destroyed ?

Thanks for your answers :)


texts: How is solar radiation pressure included in the SGP4 orbital propagator?

texts: TLE sets serve as input elements for the SGP4 orbital propagator. Several orbital perturbation effects are considered in the SGP4. However, it is not obvious to me how (or if) the solar radiation pressure is accounted for in the SGP4.


texts: Attach a visible light telescope to the outside of the ISS

texts: Visible light imaging of the heavens is limited on Earth primarily due to the atmosphere. I know the ISS is moving at 17000mph, but given the delays to the James Webb telescope, is there any merit in attaching a space-rugged visible light telescope to the outside of the ISS? Could it ever approach the visible light performance of Hubble?


texts: Details of the M87 Active Galactic Nucleus -- questions of scale

texts:
This video describes a scale model of the M87 SMBH (somewhat distorted to live in flat space and for other practical reasons) in which the Schwarzschild radius appears to be scaled to about 10cm, with the photon sphere and inner accretion disk around it. If one wanted to go further, making a somewhat larger model to the same scale along similar lines and using similar materials, what would be next features to include, and how far away are they?
I am tempted, for instance to try to model the base of the relativistic jets, using these but I'm not sure if they are big enough, or how far away they would have to be. Alternatively, are there more accretion disk features that would show up while still fitting in my dining room? Suggestions are welcome.


texts: Cross-correlations between Lagrange and Fourier synthesis

texts:
In the context of forecast for large surveys, I have to make cross-correlations between 2D (with angular coordinates of Lagrange transformation for GC photometric and Weak Lensing) and 3D (Fourier transform with radial coordinates for GC spectroscopic).
For the moment, only cross-correlation for 2D is achieved (GCph+WL+XC), or what we call 3x2 points (with XC representing the cross-correlations).
For example, a Fisher matrix element for 3x2pt is expressed as :

where $\epsilon$ ranges over G(Galaxy), L(Weak lensing) and GL(Galaxy,Weak lensing)
Could anyone tell me or give links plese about the full cross-correlations between 2D and 3D, i.e GCsp+GCph+WL+XC (4x2 points) in the litterature ?
Beyond a complicated theorical formula, I prefer to know more about the state of the art.
I mean, I would like to know what has been already done in this attempt of cross-correlation 2D+3D.
One told me there are been Bessel-Fourier works or some similar stuff but I would like to have more informations about this.
Any help is welcome


texts: Apparent Centering Problem When Using the Perifocal System to Draw Orbital Ellipses

texts:
I am attempting to render orbital ellipses in software.  Given a set of orbital elements, I am using the Perifocal system to determine a set of points along the curve of the ellipse.  I am using the equation:
r = r cos(v) P + r sin(v) Q,
where v is the angle, P and Q are the perifocal vectors correspondent to I and J, and r is the polar equation of the conic:
r = p / 1 + e cos(v),
where p is the semi-latus rectum, e is eccentricity, and v, in both equations, is the angle.
I am determining the vectors P and Q using the following equations:
Pi =   cos (lan) cos (aop) - sin (lan) cos (inc) sin (aop)
Pj =   sin (lan) cos (aop) + cos (lan) cos (inc) sin (aop)
Pk =   sin (inc) cos (aop)

Qi = - cos (lan) sin (aop) - sin (lan) cos (inc) cos (aop)
Qj = - sin (lan) sin (aop) + cos (lan) cos (inc) cos (aop)
Qk =   sin (inc) cos (aop)

where lan is the Longitude of Ascending Node, aop is the Argument of Periapsis, and inc is the inclination.
This process yields the correct ellipse!  However, the ellipse does not seem to be centered correctly on its focus; the focus appears to be far too close to the center of the ellipse.  Here is an example:

You can see that these two highly eccentric ellipses have their shared center of mass at their centers - not at their respective foci.
Is there some step in my process that I'm missing?  I could just apply an offset to the ellipses, but that would be a hack, I want to solve the problem.
Any help is appreciated!  Thank you!
QUESTION EDITS AND CLARIFICATIONS:
This image is taken from a vantage point nearly normal to the orbital plane; there is almost no perspective here.
Second, a helpful user has pointed out an issue in the equation for Pk. The correct expression is:
Pk = sin (inc) sin (aop)
Unfortunately, this was correct in my code - so while the correction was a good one, it was not the source of my problems.


texts: Why does the concentration-mass relation of galaxy clusters have a negative slope?

texts:
As reported in some recent observational works works (ref. Merten et al. 2015) the concentration-mass relation of galaxy clusters has a negative slope. This means that at a fixed redshift, haloes with a higher mass have a lower concentration.

Some old works say this is a consequence of the fact that the concentration depends only on the density at the assembly time. For instance, Bhattacharya et al. 2013  says:

  The correlation of halo concentration with mass is based on the idea—as first explicated by NFW—that the concentration is determined by the mean density of the universe when the halo is assembled, with higher concentrations corresponding to higher densities. Thus cluster mass halos, which are assembling today, should have a lower concentration than halos of lower mass that were built up at an earlier epoch, where the mean density was higher. Furthermore, one may expect this trend to flatten out (sufficiently) beyond the nonlinear mass scale $M_∗$, and therefore, since $M_∗$ falls rapidly with redshift, flatten out over an extended range in mass as redshift increases.

I cannot understand how this can lead to a negative slope between the concentration and the mass


texts:
The definition of flux and flux density is fairly straightforward. However, I'm musing over the practical usage of it.

For one thing, if you observe a source through a filter, how would one go from the total observed energy/number of photons to the flux per unit wavelength? It's not a matter of simply dividing by the width of the filter -- a filter can have any exotic form of course.

So, how is this derived?
Related, given a $f_{\nu}$ in some filter, what would be the way to go to total flux within that filter?


texts:
What does the image in the link mean?  Are the stars in the halo high in metallicity or low?  How about at the bottom by the disk?

http://science.psu.edu/alert/images/SDSSmetals.jpg/image_view_fullscreen


texts: What is the ratio of "real" stars in the sky?

texts:
When you look at the sky without any utilities like binocular or telescope, what is the rough ratio of "real" stars to other objects like planets, the moon, asteroids, satellites?

90% stars - 10 % others?
99% stars - 1% others?
Almost 100% stars - apart from a very few you can easily name as a hobby astronomer?


texts: Supposed SN 1006 was only 4 lightyears away what would the blasts impact be like on earth?

texts:
One of the commenters on my answer to https://worldbuilding.stackexchange.com/a/86733/3460 questions that the blast would even have a noticeable impact if that supernova was in Alpha Centauri. And since my answer is just based on my intuition, I would like to figure that out.

So radiation put aside, what would the blast of SN 1006 be like for earth when arriving, supposed it went supernova just 4 light-years away?


texts: Function for current distance between in light-seconds between Mars and Earth

texts:
I'm looking for a function that given a time (for example Unix time) gives back the current distance between Mars and Earth in light-seconds.

It can be a mathematical function or programming function (preferably in Python or pseudocode), but must not rely on an Internet connection.

This question is similar to a question I asked erlier, but again I need to get the distance without an Internet connection.

Thanks in advance!

Sidenote: I'm planning on learning orbital mechanics, but I need this function earlier. :)


texts:
I have looked into Lagrange points a decent amount and I see many images that show the L4 and L5 locations as wide sweeping areas. Jupiter's Trojan asteroids are a good example of this. As well, L3 sometimes is shown inset of the Hill Sphere [but that is another question]. I assume that each point is an infinitely small point in space at the exact mathematical position (ignoring any other gravitational affects that might be there).

My question: is there a way to determine the "stable" region in each Lagrange location?
Particularly in the L4 and L5 regions.

Essentially, I would like to be able to know how much additional thrust a craft might need to stay at these locations depending on how far away they are from the center of the Lagrange point.


texts: As we all know, antimatter is present across all of space. Is it also present on Earth? If it is present on Earth then by the interaction of matter and antimatter, why don't we feel the energy around us?


texts: Did Earth "tilt" seasonally before it was accepted that the world was not flat?

texts: Before it was widely accepted that the Earth was round, how did astronomers describe the yearly movement of the sun to south in the Northern Winter that produced the seasons? Did the Earth wobble or did the Sun just not have a perfectly circular trajectory around the Earth? Did this perspective change when we realized the Earth was a globe? What about before Heliocentrism was the norm?


texts: Why isn't the constellation of that month's zodiac prominent or even visible during that month?

texts: For instance, the month of October is called the month of Leo, but you will mainly see Aries, Taurus and the Southern skies during October, Leo isn't very prominent. So how is the zodiac decided?


texts: How to calculate the statistically significant level for a guassian line profile?

texts:
In some papers, they fit a line profile with gaussian model. For example, in
this paper, fig 1 draw three gauss line profile, O VII, O VIII, and Ne IX.
But the data seems noisy and the gaussian height (from bottom to the top of the gauss line, especially O VIII, and Ne IX) do not seems above 3*(the height of 1-sigma errorbar) of the residual data. But in the text they say (on the left bottom of page 3): "The centroid wavelengths of three lines are consistent with O VII, O VIII, and Ne IX at zero redshift,respectively. Those lines are statistically significant at the 6.5, 3.1, and 4.5 sigma levels.". So i'm puzzled with the calculation algorithom of the significance. In my memory that the sigma=sqrt(variance of the residual data) and the height of gauss Intensity=exp(a*(x-b)/c^2), the significance = a/sigma. Then any wrong with my calculation?


texts: Is all of the data from the same program that found the Wow!-signal analyzed?

texts:
I just read on Wikipedia that...

  By 1977, Ehman was working at the SETI project as a volunteer; his job involved analyzing by hand large amounts of data processed by an IBM 1130 computer and recorded on line printer paper.

Emphasis mine.

From what I understand, the program had been running for four years before this happened, (1973–1995), and considering the amount of data that must have been generated and how bad humans are at doing boring repetitive tasks, it seems to me that the risk is very high that a similar event was overlooked. Here is a small example of the type of printouts he was looking at:

You can easily imagine a stream of 5IJSI in one of the 50 columns looking the same as 21121 to a tired human operator.

So I have two related questions:

Was manual human inspection the only analysis done on the data during the seventies, or did he just do it out of interest? Was the program set up to alert on any "suspicious" signals, for example anything above a certain threshold for at least two samples?
Is all data digitally preserved? I assume that by the eighties, everything became trivial to store, but I'm not so sure everything was stored in the seventies when they just started. If the data is preserved, has further automated analysis been done on the data set before and after the Wow!-event to rule out anything similar?


texts: How are the numerical stellar subclassifications determined?

texts:
From Wikipedia:

  The spectral classes O through M, as well as other more specialized classes discussed later, are subdivided by Arabic numerals (0–9), where 0 denotes the hottest stars of a given class. For example, A0 denotes the hottest stars in the A class and A9 denotes the coolest ones. Fractional numbers are allowed; for example, the star Mu Normae is classified as O9.7. The Sun is classified as G2.

So our Sun is a G2V yellow dwarf.

The G identifies its temperature as within the range of 5,200-6,000K.
The V tells us it is on its main sequence.

That leaves us with the 2. The 2 tells us that the sun is warmer than a G3 star and cooler than a G1. I get that. My problem: I just can't seem to figure out how the ranges of these specific numerical subclasses are determined. Are they explicitly defined? Logarithmic? Is there a way to calculate it exactly? Why is Mu Normae a O9.7?

My best guess is to take the range of the stellar class and divide it into 10 subsections but I can't find any source to confirm that.


texts: I know that after a star undergoes the process of mass loss, depending on the mass of the core the stellar remnants gets converted into a white dwarf star, neutron star or a black hole. Hence, if the mass of the stellar remnant exceeds the Tolman–Oppenheimer–Volkoff limit, then it gets converted to a black hole. So is there currently any equation which helps us to calculate the amount of time taken by the leftover core to get converted to a black hole or the rate at which the mass is gravitationally collapsing?


texts: Deducing distance of closest neighbor galaxy from expression of correlation and mean galaxy density

texts:
The original post was on physics exchange but I prefer to move it here :

I am trying to estimate the distance of closest galaxy neighbor knowing the expression of number of neighbors $\text{d}N$ into a volume $\text{d}V$, the mean density $n_\text{gal}$ and the correlation function, i.e with this expression:

$$\text{d}N=n_{\text{gal}}\,\text{d}V\,(1+\xi(r))$$

with $\xi(r)=\bigg(\dfrac{r}{r_{0}}\bigg)^{-\gamma}\quad\text{with}\quad\gamma\,\sim\,1.77 \quad\text{and}\,r_{0}\,\sim\,5\,\text{Mpc}$.

I must precise that expression of $\xi(r)$ is valid for $r$ between $0.5\,\text{and}\,10\,\text{Mpc}$

I take into my calculation the following value for $n_{\text{gal}}=0.0420\,\text{h}^{-3}\,\text{Mpc}^{-3}$ : I tried to choose a typical value for this density but it depends on which scale we consider (galaxy cluster, super cluster, very large scales ...), so maybe don't focus on this value.

What it interests me is to have elements to answer to the following question :
How could I infer the distance of the closest galaxy from us?

UPDATE 1: Maybe I should take the lower limit of validity for the definition of $\xi(r)$, i.e $r=0.5\,\text{Mpc}$ and so:

$$\text{d}N/\text{d}V=n_{\text{gal}}\,(1+\xi(r=0.5))$$

So I would have:

$$\text{D}_{\text{closest}}=\bigg(n_{\text{gal}}(1+(0.5/5)^{-1.77})\bigg)^{-1/3}=0.7353\,\text{Mpc}$$

But by taking $r=0.5\,\text{Mpc}$, I am already located myself like the closest neighbor was at $r=0.5\,\text{Mpc}$, am I not ?

Is this reasoning correct?

Any help is welcome


texts: How do stars or galaxies get their spin?

texts:
It is my understanding that when a star, a planetary disk, or a galaxy forms, the rotational momentum of the whole system is conserved.

Due to the smaller size of the resulting object, it will spin with a significantly higher speed than the original nebula.

What I do not understand is where the original rotation comes from. Why should a random dust cloud have an overall spin? Wouldn't the impulses of all particles in the cloud tend to average each other out?

Is there some alternative source of spin or a reason why nebula have an inherent spin?


texts: What discoveries have come from the DASCH project (Digital Access to a Sky Century @ Harvard)

texts:
@astrosnapper's answer to the question Could stellar occultations be used to survey Kuiper belt objects? mentions the TAOS-II project and asteroid occultation measurements (which occur on the timescale of seconds) and that got me thinking about the term Time Domain Astronomy.

A quick search led me to an Astrobites post with a catchy title A Big Step Backward for Time Domain Astronomy that (among other things) describes the DASCH project (Digital Access to a Sky Century @ Harvard).

The post is dated 2012 and says:

  The project is working to (1) digitally scan all of the plates, (2) detect sources on the plates, (3) assign physical coordinates to the plates, and (4) measure/calibrate the magnitudes of all sources.  The end product will be a publicly available database which can be queried to produce the 100 year light curve for individual objects.  As a part of the project the team had to develop a specialized scanner, as commercially available units would have been too slow to finish the project in anything resembling a reasonable amount of time. As it is, when operating at full efficiency, the project can now scan and analyze 400 plates a day.  As of the writing of this article, 38,346 plates have been scanned (~8% completion; see Figure 2 for a map of their current coverage) and over 2.7 billion magnitudes have already been measured.

The article ends with:

  ...Given that we’re only 8% of the way through analyzing the plates, we can look forward to further interesting discoveries from this survey in the next few years.

It is now six years later. Presumably the scan rate has accelerated a bit and a much larger fraction of the plates have been scanned, and techniques for reducing and analyzing the huge amounts of data have improved as well.

Since 2012, what new discoveries have been made from this effort? There may be too many to list, so a few highlights and a link to a summary might be the best way to answer.


texts: Do all / most / any other moons orbiting a planet synchronize their rotation so as to become tidally locked with it, or is the earth a special case?


texts: Does the accelerating expansion of spacetime mean that the pace of time is changing?

texts: Space expands everywhere, also here. And time is inseparable from space. Does this mean that time also "expands" as in changing its pace? Is the changing rate of time also astronomically observable? How did time behave during the radical inflation shortly after Big Bang?


texts: If time is not absolute and depends on the gravitational field, then why we keep using our own (particular) time in cosmology?

texts:
Sorry if my question is not really clear, but indeed it is not clear in my mind neither.
But maybe some of you can help.
Time is not absolute and can be affected by the gravitational potential.
Now the question is: do concepts like the age of the Universe, time between different cosmic epochs etc, depend on the position of the observer with respect to a gravitational field?
If yes, how much things would change if we were observers, e.g., close to a black hole or in absence of gravity?


texts: How to improve the precision in a star's distance

texts:
When I use the Gaia star catalogue, the parallax values often have large uncertainties which, therefore, leads to a large uncertainty for the distances to the stars.
If you were interested in the distance to one particular star and money was no object (i.e. you could buy time on any instrument) - what would be the optimum thing that could be done to improve the precision in the star's distance?


texts: How can the information encoded in a boundary be changed in holographic principle?

texts:
When information is encoded in a boundary of a bulk, following the holographic principle, it would raise a universe in the boundary with physics determined by the information encoded on it.

My question is: Can this information (once encoded in the boundary) be modified or changed? Can it be modified without changing nothing in the bulk?


texts: What was the bright orange glow in the sky?


texts: Viewing 2017 Solar Eclipse - How important is it to be in the center(blue line)?

texts:
I'm viewing the 2017 Solar Eclipse in Graham County, NC.  How important is it to be in the center(blue line)?

It is almost entirely national forest there so it would be fairly easy to get to assuming I can park somewhere.

http://xjubier.free.fr/en/site_pages/solar_eclipses/TSE_2017_GoogleMapFull.html


texts: What will a future cold and "dead" Jupiter look like?

texts:
I heard Jupiter is dying like getting smaller. For example, from Guillot et al. 2004 3: The Interior of Jupiter (also here):

(Jupiter)... is still contracting at the rate of ~3 cm per year while its interior cools by ~1 K per million year.

When will it completely die, how much smaller will it be then, and what will it look like?